Dynamic Coassembly of Amphiphilic Block Copolymer and Polyoxometalates in Dual Solvent Systems: An Efficient Approach to Heteroatom-Doped Semiconductor Metal Oxides with Controllable Nanostructures

Dynamic coassembly of block copolymers (BCPs) with Keggin-type polyoxometalates (POMs) is developed to synthesize heteroatom-doped tungsten oxide with controllable nanostructures, including hollow hemispheres, nanoparticles, and nanowires. The versatile coassembly in dual n-hexane/THF solvent solution enables the fomation of poly(ethylene oxide)-b-polystyrene (PEO-b-PS)/POMs (e.g., silicotungstic acid, H4SiW12O40) nanocomposites with different morphologies such as spherical vesicles, inverse spherical micelles, and inverse cylindrical micelles, which can be readily converted into diverse nanostructured metal oxides with high surface area and unique properties via in situ thermal-induced structural evolution. For example, uniform silicon-doped WO3 (Si-WO3) hollow hemispheres derived from coassembly of PEO-b-PS with H4SiW12O40 were utilized to fabricate gas sensing devices which exhibit superior gas sensing performance toward acetone, thanks to the selective gas–solid interface catalytic reaction that induces resistance changes of the devices due to the high specific surface areas, abundant oxygen vacancies, and the Si-doping induced metastable ε-phase of WO3. Furthermore, density functional theory (DFT) calculation reveals the mechanism about the high sensitivity and selectivity of the gas sensors. On the basis of the as-fabricated devices, an integrated gas sensor module was constructed, which is capable of real-time monitoring the environmental acetone concentration and displaying relevant sensing results on a smart phone via Bluetooth communication.


Table of Content
Supplementary gas sensing and computational methods (Page S2−S5) Supplementary schematic diagram of synthesis mechanism (Page S6) Supplementary structural characterizations (Page S6−S18) Supplementary experimental details of gas sensing (Page S18−19) Characterizations and gas sensing performances of mesoporous WO 3 (Page S20) Gas sensing performances of P-WO 3 , Si-MoO 3 and P-MoO 3 nanomaterials-based sensor (Page S21−23) In situ FTIR spectroscopy (Page S24) DFT calculations (Page S24−25) Tests of real-time monitoring of gas concentration on smart phone (Page S26−27)

Characterizations and measurements.
Field emission scanning electron microscopy (FESEM) was performed on a Zeiss Ultra 55 field-emission SEM (Germany) operated at 3 kV and 10 μA. Transmission electron microscopy (TEM) was conducted on a JEM-2100 F microscope (JEOL, Japan) operated at 200 kV. The samples for TEM measurements were first dispersed in ethanol and supported onto a carbon coated copper grid. Nitrogen sorption isotherms were measured at 77 K with a Micromeritics Tristar 3020 analyzer. Before measurements, the samples were degassed in vacuum at 180 °C for at least 6 h. The specific surface area and the pore size distribution were calculated by using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) method, respectively. The total pore volume (V total ) was calculated from the adsorption volume at P/P 0 = 0.995. Fourier-transform infrared (FTIR) spectra were collected on a Nicolet Fourier spectrophotometer using KBr pellet method. Powder X-ray diffraction (XRD) patterns were recorded on Bruker D4 X-ray diffractometer (Germany) equipped with Ni-filtered Cu Kα radiation (40 kV, 40 mA). The X-ray photoelectron spectroscopy (XPS) spectra were collected on an RBD 147 upgraded PHI 5000C ESCA system with a dual X-ray source. The Mg Kα (1253.6 eV) anode and a hemispherical energy analyzer were used in the measurements. All of the binding energies were referenced to the C 1s peak at 284.8 eV of the surface adventitious carbon. The average sizes of micelles were tested using a dynamic light scattering (DLS) instrument (Malven, Zetasizer Nano ZS, UK).

Gas sensing tests
Before the tests, the Si-WO 3 hollow hemispheres powder was mixed with ethanol and grounded in an agate mortar to form a paste. The resulting paste was coated on an alumina tube on which a pair of Au electrodes had been printed previously, followed by drying at 100 °C for about 2 h and subsequently annealing at 250 °C for about 2 h. Finally, a small Ni-Cr alloy coil was inserted into the tube as a heater to adjust and optimize the working temperature of the gas sensor. To improve the long-term stability, the sensors were kept at the working temperature for 3 days. The gas sensing performance of the fabricated Si-WO 3 S3 sensors was performed using a dynamic gas distribution test system (JF02F, China). The gas sensing response (S) in the measurement was deduced using the following equation, S=R a /R g , where R a and R g are the resistance of materials in air and in the test gas, respectively. In addition, the gas sensing performance working at different temperatures was investigated to find the optical working temperature, which is determined by the voltage of the heating electrode. The commercial acetone gas was purchased from Shanghai Weichuang Company.
The acetone in the dry air with an accurate concentration can be controlled by the gas distribution box.

Computational methods
First-principles were used to describe the ions behavior in the anode based on density functional theory (DFT) with the Vienna ab initio simulation package (VASP) code. In addition, Perdewe-Burkee-Ernzerhof (PBE) generalized gradient approximation and the projected augmented wave (PAW) method were used to describe the ion-electron interactions in our systems. In this study, the plane-wave cutoff energy was set to 450 eV, and van der Waals corrections (optPBE-vdW) were adopted during structural optimization for the layer materials, and the vdWs interactions were described exactly by using DFT-D3 correction method of Grimme's scheme. Partial occupancies of the Kohn−Sham orbitals were allowed using the Gaussian smearing method and a width of 0.05 eV. The electronic energy was considered self-consistent when the energy change was smaller than 10 −6 eV. A geometry optimization was considered convergent when the energy change was smaller than 0.05 eV Å −1 . The vacuum spacing in a direction perpendicular to the plane of the structure is 15 Å.
The Brillouin zone integration is performed using 3×3×1 Monkhorst-Pack k-point sampling for a structure. Finally, the adsorption energies (E ads ) were calculated as E ads = E ad/sub -E ad -E sub , where E ad/sub , E ad , and E sub are the total energies of the optimized adsorbate/substrate system, the adsorbate in the structure, and the clean substrate, respectively.

Principle of wireless gas sensor module
The circuit diagram of the wireless gas sensor module is as follows:

S4
The inverting amplifier can convert the resistance information into voltage information. The operational amplifier OPA376 (Texas Instrument, TI) was adopted in the system, which provides extremely high input impedance and rail to rail input/output range. MUX (multiplexer) is connected to the feedback resistance of the inverting amplifier as a switch, which can change the measuring range of the resistance. In this system, ADG704 from Analog Devices Company is adopt as MUX to provide extremely low on-resistance (<8 Ω) to ensure measurement accuracy, and extremely low leakage current (<0.3 nA) to ensure large resistance measurement in the order of GΩ.
ADS1115 from TI Company was adopted as the Analog to Digital Converter (ADC). The ADC was integrated with a differential input Programmable Gain Amplifier (PGA), which can be used to realize voltage subtraction calculation. The voltage is collected by ADC and processed by Micro Controller Unit (MCU). The resistance value can be calculated and the concentration can be fitted, which can be sent to the smart phone via Bluetooth.
In addition, the heating power of the heating resistor can be controlled by Pulse Width Modulation (PWM), and the heating current can be collected by measuring the voltage of the resistor in series, and the data can be sent to the MCU for power management or sent to a smart phone.

S5
According to the schematic, in which, V out is the output voltage, V ref1 is the voltage reference, R x is the resistance value of gas sensor, and V cc is the supply voltage.

The voltage collected by ADC is
where A PGA is the voltage gain of PGA inside ADS1115.
When the resistance to be measured is too small, the voltage measured by the ADC is relatively large. The measurement range of the circuit can be adjusted by reducing the PGA gain A PGA , or switching the reference resistance through MUX (reducing the value of R ref ).
When the resistance to be measured is too large, the voltage measured by the ADC is low.
The measurement range of the circuit can be adjusted by increasing the PGA gain A PGA , or switching the reference resistance through MUX (increase the value of R ref ).               ppm.